The present invention generally relates to luminaires of the type most often used in architectural spaces, and more particularly to luminaires having a downlight component and an exposed light source having exposed high brightness surfaces that can produce visual discomfort and glare. The invention has particular application in luminaires having small dimensioned high-intensity lamps, such as a high-output T5 fluorescent lamp.
A wide range of luminaires have been designed to meet a variety of architectural lighting applications, including luminaires that provide direct lighting, indirect lighting, and a combination of both indirect and direct lighting. In the case of direct luminaires and luminaires for direct/indirect lighting, the source of illumination is either exposed in its entirety through the bottom of the luminaire or shielded by shielding elements such as parabolic baffles or lenses that cover the bottom opening of the luminaire. The choice of luminaire will depend on the objectives of the lighting designer for a particular application and the economic resources available. To meet his or her design objectives, the lighting designer, when choosing a luminaire, will normally consider a variety of factors including aesthetic appearance, desired light distribution characteristics, and sources of brightness that can detract from visual comfort.
Another important factor in selecting luminaires for a particular application is the choice of a light source. In this regard, the fluorescent lamp has long provided an economical and energy efficient alternative to incandescent lighting and has been the light source of choice among lighting designers in many commercial applications, particularly for indoor office lighting. For many years the most common fluorescent tube sizes for use in indoor lighting have been the T8 (1 inch diameter) and T12 (1xc2xd inch diameter) lamps. More recently, however, smaller dimensioned, high-output fluorescent lamps have become available which provide a high lumen output from a comparatively small lamp envelope. An example is the high output T5 (⅝ inch diameter) lamp manufactured by Osram/Sylvania and other manufacturers. This fluorescent lamp has a number of advantages over its larger predecessors, the T8 and T12, including the ability to design luminaires which produce a high lumen output with fewer lamps reducing lamp disposal requirements and even potentially lamping costs as the cost of high output T5 lamps comes down. The smaller diameter T5 lamps also permit smaller luminaires to be designed. They further allow the designer to achieve greater control over light distribution because of the small light emitting surface areas involved. As a consequence, wider light distribution patterns can be achieved permitting greater spacing between luminaires without sacrificing coverage and lighting uniformity.
High-output compact fluorescent lamps, however, have a significant drawback: the lamp surfaces are extremely bright as compared to larger diameter lamps. For example, a high-output T5 lamp will have a surface brightness in the range of 8,000 footlamberts (FL), whereas the brightness of the larger T8 and T12 lamps will be in the range of 3,000 FL and 2,000 FL, respectively. The consequence of such bright surfaces is quite severe in downlight applications where the lamps may be exposed within direct viewing angles. Without adequate shielding, fixtures employing such lamps will be very uncomfortable to look at directly, and will produce direct and reflected glare that impairs the comfort of the lighting environment. Heretofore, shielding has been devised to cover or substantially surround a fluorescent lamp to mitigate surface brightness problems; however, such shielding defeats the advantages of a compact fluorescent lamp in regions of distribution where the lamp""s surfaces are not directly viewed or do not set up reflected glare patterns. Thus, with conventional shielding designs, the distribution efficiencies and high lumen output advantages of the compact lamp can be substantially lost. Another known approach to solving the problem of direct glare associated with the use of high intensity fluorescent lamps in downlight applications has resulted from the use of biax lamps in direct-indirect luminaires. This approach has been to use the biax lamps only for the uplight component of the luminaire while using T-8 lamps with their lower brightness surfaces for the luminaire""s down-light component. However, such design approaches have the drawback that the extra lamps impair they designers ability to achieve a desired light distribution from a given physical envelope and impose added burdens on lamp maintenance programs which must stock and handle two different types of lamps.
The present invention overcomes the above-described disadvantages of high-output light sources by providing a mock light source in the downlight opening of a luminaire which, from the point of view of the downlight opening, behaves like a larger lamp size having a larger, lower brightness surface area, but which otherwise permits the luminaire to take advantage of the distribution and output efficiencies of the small dimensioned high-output lamp. For example, a luminaire having a mock light source in accordance with the invention permits a direct-indirect luminaire to be designed using one or more high output T5 fluorescent lamps where the luminaire""s uplight distribution is advantageously produced directly from the lamp""s extremely bright, relatively small surfaces, while the downlight component of the luminaire is produced principally from a mock lamp that behaves and looks like a T8 or T12 lamp having surface brightness characteristics that are three to four times less than the T5 lamp. Because the downlight opening sees a mock lamp having more conventional lamp dimensions with more conventional lamp brightness characteristics, conventional downlight shielding can be used without having to design special optics to account for the special characteristics of an extremely bright high intensity source. At the same time the problem of distracting direct glare associated with high intensity sources being used in the downlight opening of a direct or direct-indirect luminaire is reduced. This is accomplished without the addition of lamps and the added costs associated therewith.
In summarizing and describing the invention, reference will be made to an xe2x80x9cactivexe2x80x9d light source as distinct from a xe2x80x9cmockxe2x80x9d or xe2x80x9cpassivexe2x80x9d light source which is intended to simulate an active light source. The xe2x80x9cactivexe2x80x9d light source shall be understood to mean the energized lamp or lamps which generate the actual lumen output of the luminaire.
Briefly, the invention involves a luminaire which comprises a housing having a downlight opening, an active light source operatively held in the housing above the downlight opening, and a brightness reduction cover element operatively positioned in the housing below and in proximity to the bottom surface portion of the light source so as to intercept light emitted therefrom. The brightness reduction cover element is sized and shaped to cover the bottom surface portion of the light source to substantially the minimum extent necessary to prevent line-of-sight exposure of the active light source through the housing""s bottom opening and to the extent necessary to provide an observable source of reduced brightness just below the active light source which simulates a lower brightness source of light. Other surface portions of the light source not covered by the brightness reduction cover element remain available to contribute directly to the overall lumen output of the luminaire. The brightness reduction cover element can be positioned directly above, and at least in part supported by a baffle structure which shields the cover element from direct view at high viewing angles and which controls the distribution of light passing through the housing""s downlight opening.
In one embodiment of the invention, the brightness reduction cover element is provided in the form of a light diffuser cover strip that provides a uniformly bright surface and that has an elongated arcuate shape to simulate the surface of a larger diameter fluorescent tube. Alternatively, the brightness reduction element could be fabricated of a perforated sheet metal material having small openings which provide an average reduced brightness to the observer. To reduce spot brightness at its perforation openings, a diffuser liner can, if desired, be affixed to at least one surface of the perforated sheet material.
The following are specific examples of a brightness reduction element for use in a luminaire having a T5 high-output active light source: an elongated arcuate-shaped opal diffuser cover strip having a radius of approximately xc2xe inch to simulate a 1xc2xd inch diameter T12 fluorescent lamp, and a similarly shaped diffuser cover element having a radius of approximately xc2xd inch to simulate a 1 inch diameter T8 fluorescent lamp. Other shapes and sizes can also be chosen to meet the particular needs of the lighting designer, including a trough-shaped or triangular-shaped diffuser cover element to simulate the appearance of a fluorescent lamp that has a square or triangular shape. The composition of the opal diffuser material used to fabricate the cover strip can be chosen to simulate a desired whiteness.
In a further aspect of the invention, the luminaire is provided in the form of a direct/indirect luminaire having a housing with both uplight and downlight openings. The brightness reduction cover element, which again is positioned below and in proximity to the bottom surface portion of the active light source, permits an observable source of reduced brightness to be exposed through the housing""s downlight opening while permitting the uplight portion of the luminaire to be governed by the high lumen output from the top surface portion of the smaller active light source. While the invention has particular applicability in this luminaire type, it could also be used in a purely direct luminaire where the high lumen output from the top surface portion of the active light source is redirected by internal optical components of the luminaire through the downlight opening of the luminaire housing.
In still another aspect of the invention, the brightness reduction cover element is replaceably held in its operative position within the luminaire such that cover elements can readily be exchanged to permit modification of the luminaire""s brightness and/or color characteristics to meet particular lighting design and application needs.
The invention also involves a method of producing direct and indirect lighting from an active high output light source, such as a T5 lamp, having top and bottom surface portions with relatively high surface brightness. The method comprises the steps of producing uplight for indirect lighting directly from the top surface portion of the light source, and producing downlight for direct lighting through a brightness reduction cover element positioned below and in close proximity to the light source""s bottom surface. The brightness reduction cover element is sized and shaped to surround the bottom surface portion of the light source so as to simulate a relatively low brightness light source having a larger surface area than the surface area of the active high output source.
It is therefore a primary object of the invention to provide a direct or direct-indirect luminaire having a mock light source for improved source brightness control. It is a further object of the invention to provide a luminaire and method which can take advantage of compact, high-output light sources without introducing excessive brightness into an architectural space. It is a further object of the invention to provide a luminaire having a compact high-output light source wherein light emitted from the bottom surfaces of the light source is intercepted for source brightness control, while light emitted from the top surfaces of the light source is available for improved lumen output and light distribution from the luminaires It is still another object of the invention to provide a luminaire and method which can utilize compact, high-output light sources while at the same time permitting the use of conventional parabolic baffles or other conventional shielding designs in the downlight opening of the luminaire.
Other objects of the invention will be apparent from the following description and claims.